• Proceedings of the KIEE Conference
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• 2001.07a
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• pp.190-193
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• 2001

This paper presents a linear programming based Optimal Reactive Power Dispatch (ORPD) problem using modified sensitivity method. The proposed model minimizes the real power losses and improves the voltage profiles in the system with consideration of voltage and reactive power constraints. The method employs modified sensitivity relationships of power systems to establish both the objective function for minimizing the system losses and the system performance sensitivities relating dependent and control variables. The proposed algorithm has been evaluated with the IEEE 6-bus and IEEE 30-bus systems.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.1902-1904
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• 1998

In this paper. a noble dead time minimization algorithm is presented for reducing the switching losses. Firstly, the effects of the inverter dead time are examined, Secondly the principle of the proposed algorithm is explained with the commutation conditions. And the validity of the proposed algorithm is verified by simulation results. We can conclude from the results that the proposed algorithm have a virtue which is able to reducing the hamonics in the output voltages and which make the output voltage equal to the reference vlaue. Another merit is this method can reduce the number of inverter switchings.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1265-1266
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• 2006

Multi-stacked HTS tapes are needed to conduct large current in the power application of superconducting machine. This paper deals with the transport current loss of multi-stacked YBCO coated conductor. YBCO coated conductor that was used in this experiment has two Cu layers above and below of YBCO layer for stabilization. Transport losses of four different stacks, single, 2 stack, 3 stack and 4 stack, were measured. Measured results were compared analytic equation suggested by Norris.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.276-280
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• 2003

This paper presents a zero voltage and zero current switching (ZVZCS) interleaving two-transistor forward converter for high input voltage and high power application. A phase shift has a disadvantage that a circulating current and RMS current stress, conduction losses of transformer and switching devices increases. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved interleaving two-transistor forward Zero Voltage and Zero Current Switching (ZVZCS) dc/dc converter using a tapped inductor a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 1.8kW, 5kHz experimental prototype.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.427-433
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• 2004

The effects of flow interaction between mainstream and shrouded cavity leakage flow in an axial-flow compressor on aerodynamic losses are experimentally and numerically examined. A fraction of mainstream is Ingested in the downstream cavity and travelled in the shrouded cavity along the direction opposite to the mainstream. This leakage flow is caused by adverse pressure gradient along the blade passage. Then it is entrained through the upstream cavity near mid-pitch and interacts with the mainstream. As a result, the convection flow angle with respect to the blade chord is reduced i.e. underturning This underturned flow results in an increase in size of secondary flow formed near the suction side of the blade as well as its magnitude. Consequently, this causes pronounced increase in overall aerodynamic losses compared to the blading without shrouded cavity, leading to $9\%$ decrease in pressure rise through the single stage of the stators.

• Journal of Magnetics
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• v.19 no.2
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• pp.146-150
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• 2014

The objective of this paper is to provide a comparison between two transverse flux rotary machines (TFRM) with different topologies of stator cores. Depending on how to make stator core with laminated steel sheets, the one topology is 'perpendicular stacking core' and the other is 'separated core'. Both of the two cores have been designed considering 3-dimensional (3-D) magnetic flux path with the same output power conditions, but the core losses are quite different and it causes different magnetic and thermal characteristics. For comparison of these two topologies of stator cores, therefore, core losses have been calculated and used as a heat source in no-load conditions, and the thermal stress has been also calculated. 3-D finite element method has been used for the magnetic field, thermal, and stress analysis to consider the 3-D flux path of the TFRM. After comparing the analysis results of the two topologies, experimental results are also presented and discussed.

• Proceedings of the Safety Management and Science Conference
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• 2010.04a
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• pp.219-230
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• 2010

Remarkably improvements have occurred recently in the maintenance management of physical assets and productive systems, so that less wastages of energy and resources occur. The technology of maintenance is about finding and applying cost-effective ways of avoiding or overcoming performance deterioration. Maintenance is thus a vital support function in business, especially as increasingly large investments are being required in physical assets. TPM(Total Productive Maintenance) focuses on optimizing planning scheduling. Availability, performance and quality rate are other factors that affect productivity. Especially there are some losses that affect the overall equipment effectiveness(OEE). These losses lead to low values of OEE, which provides an indication of how effective the production precess is. This study explores the ways in which Korean small and medium manufacturing industries can improve OEE.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1188-1194
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• 2008

To cope with the demagnetization risk of permanent magnets used in Interior Permanent Magnet Synchronous Motors(IPMSM), an accurate iron analysis and thermal analysis are very important. In this research, to calculate thermal increment of IPMSM for high-speed traction motor, we will extract losses of IPMSM considering the condition of field weakening control. Then we will input the calculated losses such as iron loss and copper loss as the thermal sources. Based on magnetic filed and thermal analysis, we will support the design of IPMSM for high-speed train.

• Computational Structural Engineering : An International Journal
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• v.2 no.1
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• pp.11-17
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• 2002

Cost-effectiveness in design is considered for determining the target reliability of concrete bridges under seismic actions. This objective can be achieved based on the economic optimization of the expected life-cycle cost of a bridge, which includes initial cost, direct losses, and indirect losses of a bridge due to strong earthquakes over its lifetime. A separating factor is defined to consider the redundancy of a transportation network. The Park-Ang damage model is employed to define the damage of a bridge under seismic action, and a Monte Carlo method based on the DRAIN-2DX program is developed to assess the failure probability of a bridge. The results for an example bridge analyzed in this paper show that the optimal target failure probability depends on the traffic volume carried by the bridge and is between 1.0×10/sup -3/ to 3.0×10/sup -3/ over a life of 50 years.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.4
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• pp.14-19
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• 2005

In general, cell transmission delay is more sensitive for real time video service rather than cell losses in a wireless ATM network. Existing handoff schemes, which are emphasizing the prevention of cell losses, have limitations in cell transmission delay to satisfy QoS. In this paper, we propose a scheme to minimize transmission delay generated during the handoff and to maintain the sequence of cells. Transmission delay can be reduced by transmitting ATM cells with low CLP(i.e., CLP=0) prior to others and by discarding cells with high CLP(i.e., CLP= 1). The simulation results show that the proposed scheme is suitable for delay sensitive real time VBR service as well as fast handoff by giving high CLP to less meaningful MPEG frames.